General Description Features The is a 380 KHz fixed frequency monolithic step down switch mode regulator with a built in internal Power MOSFET. It achieves 2A continuous output current over a wide input supply range with excellent load and line regulation. The device includes a voltage reference, oscillation circuit, error amplifier, internal PMOS and etc. The PWM control circuit is able to adjust the duty ratio linearly from 0 to 100%. An enable function, an over current protection function and a short circuit protection function are built inside. An internal compensation block is built in to minimize external component count. The serves as ideal power supply units for portable devices. 5 2A Constant Output Current 5 140mΩ R DSON Internal Power PMOSFET Switch 5 Up to 95% Efficiency 5 Fixed 380KHz Frequency 5 Wide 3.6V to 20V Input Voltage Range 5 Output Adjustable from 1.222V to 18V 5 Built in Frequency Compensation 5 Built in Thermal Shutdown Function 5 Built in Current Limit Function 5 SOIC-8 Package is Available 5 The minimum dropout up to 0.3V Applications 5 Portable DVD 5 LCD Monitor / TV 5 Battery Charger 5 ADSL Modem 5 Telecom / Networking Equipment Figure 1 Package Type of 1
Pin Configurations Figure 2 Pin Configuration of (Top View) Pin Description Pin Number Pin Name Description 1,6, 8 NC Not Connect. 2 Vin 3 SW 4 GND 5 FB 7 EN Ordering Information Supply Voltage Input Pin. operates from a 3.6V to 20V DC voltage. Bypass Vin to GND with a suitably large capacitor to eliminate noise on the input. Power Switch Output Pin. SW is the switch node that supplies power to the output. Ground Pin. Care must be taken in layout. This pin should be placed outside of the Schottky Diode to output capacitor ground path to prevent switching current spikes from inducing voltage noise into. Feedback Pin. Through an external resistor divider network, FB senses the output voltage and regulates it. The feedback threshold voltage is 1.222V. Enable Pin. EN is a digital input that turns the regulator on or off.drive EN pin high to turn on the regulator, drive it low to turn it off. X X Circuit Type Packing Blank: Tube R: Type and Reel Package P: SOP8 2
Function Block Figure 3 Function Block Diagram of Absolute Maximum Ratings Parameter Symbol Value Unit Input Voltage V IN -0.3 to 20 V Feedback Pin Voltage V FB -0.3 to Vin V Enable Pin Voltage V EN -0.3 to 12 V Switch Pin Voltage V SW -0.3 to Vin V Power Dissipation P D Internally limited mw Operating Junction Temperature T J 150 ºC Storage Temperature T STG -65 to 150 ºC Lead Temperature (Soldering, 10 sec) T LEAD 260 ºC ESD (HBM) 2000 V Note1: Stresses greater than those listed under Maximum Ratings may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation is not implied. Exposure to absolute maximum rating conditions for extended periods may affect reliability. 3
Recommended Operating Conditions Parameter Symbol Min. Max. Unit Input Voltage V IN 3.6 20 V Operating Junction Temperature T J -40 125 ºC Operating Ambient Temperature T A -40 85 ºC Electrical Characteristics V CC = 12V, T a = 25 unless otherwise specified. Parameters Symbol Test Condition Min. Typ. Max. Unit Input voltage V IN 3.6 20 V Shutdown Supply Current I STBY V EN =0V 30 90 ua Supply Current I CC V EN =2V, V FB =1.3V 3.6 4 ma Feedback Voltage V FB V IN = 3.6V to 23V 1.21 1.222 1.26 V Feedback Bias Current I FB V FB =1.3V 0.1 0.5 ua Switch Current Limit I LIM 3 4 A Oscillator Frequency F OSC 320 380 440 KHz Frequency of Current Limit or Short Circuit Protection F OSC1 V FB =0V 42 KHz EN Pin Threshold V EN 0.7 1.2 1.7 V EN Pin Input Leakage I H V EN =2.5V -0.1-1 ua Current I L V EN =0.5V -3-10 ua Internal PMOS R DSON R DSON V IN =12V, V FB =0V V EN =12V, Iout=2A 140 mω Max. Duty Cycle D MAX V FB =0V, I SW =0.1A 100 % Efficiency η V IN =12V,Vout=5V Iout=2A - 92 - % Thermal Shutdown T OTSD 165 ºC 4
Typical Performance Characteristics Figure 4. Switching Frequency vs. Temperature Figure 5. Vfb vs. Temperature Figure 6. Icc vs. Temperature Figure 7. Efficiency vs. Load (Vin=10V) 5
Typical Application Circuit R2=2K R1=6.2K 5V2A 5.5V~20V DC INPUT Fig8. Typical Application Circuit @ 5V/2A R2=3.6K R1=6.2K 3.3V2A 4.5V~20V DC INPUT Fig9. Typical Application Circuit @ 3.3V/2A 6
R2=2K R1=6.2K 5V2A 5.5V~20V DC INPUT Fig10. Typical Application Circuit (with ceramic output capacitor) @ 5V/2A R2=3.6K R1=6.2K 3.3V2A 4.5V~20V DC INPUT Fig11. Typical Application Circuit (with ceramic output capacitor) @ 3.3V/2A 7
Schottky Rectifier Selection Guide Vin (Max) 20V 2A Load Current Part Number Vendor B220 1 SK23 6 SR22 6 Table 1 lists some rectifier manufacturers. No. Vendor Web Site 1 Diodes, Inc. www.diodes.com 2 Fairchild Semiconductor www.fairchildsemi.com 3 General Semiconductor www.gensemi.com 4 International Rectifier www.irf.com 5 On Semiconductor www.onsemi.com 6 Pan Jit International www.panjit.com.tw Table 2 Schottky Diode manufacturers. Output Voltage VS R1, R2 Resistor Selection Guide Vout = (1+R1/R2)*1.222V Vout R1 R2 1.8V 3.9K 8.2K 2.5V 3.2K 3K 3.3V 6.2K 3.6K 5V 6.2K 2K 9V 13K 2K 12V 16K 1.8K Table 3. Vout VS. R1, R2 Select Table 8
Function Description Pin Functions V IN This is the positive input supply for the IC switching regulator. A suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator Gnd Circuit ground. SW Internal switch. The voltage at this pin switches between (V IN V GS ) and approximately 0.5V, with a duty cycle of approximately V OUT / V IN. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept a minimum. FB Senses the regulated output voltage to complete the feedback loop. EN Allows the switching regulator circuit to be shutdown using logic level signals thus dropping the total input supply current to approximately 30uA. Pulling this pin below a threshold voltage of approximately 0.7 V turns the regulator down, and pulling this pin above 1.3V (up to a maximum of 12V) shuts the regulator on. For automatic starup condition, can be implemented by the addition of a resistive voltage divider from VIN to GND. Thermal Considerations The is available in SOP8 package. The SOP8 package needs a heat sink under most conditions. The size of the heat sink depends on the input voltage, the output voltage, the load current and the ambient temperature. The junction temperature rises above ambient temperature for a 2A load and different input and output voltages. The data for these curves was taken with the (SOP8 package) operating as a buck-switching regulator in an ambient temperature of 25 o C (still air). These temperature rise numbers are all approximate and there are many factors that can affect these temperatures. Higher ambient temperatures require more heat sinking. For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (Once exception to this is the output (switch) pin, which should not have large areas of copper.) Large areas of copper provide the best transfer of heat (lower thermal resistance) to the surrounding air, and moving air lowers the thermal resistance even further. Package thermal resistance and junction temperature rise numbers are all approximate, and there are many factors that will affect these numbers. Some of these factors include board size, shape, thickness, position, location, and even board temperature. Other factors are, trace width, total printed circuit copper area, copper thickness, single or double-sided, multi-layer board and the amount of solder on the board. The effectiveness of the PC board to dissipate heat also depends on the size, quantity and spacing of other components on the board, as well as whether the surrounding air is still or moving. Furthermore, some of these components such as the catch diode will add heat to the PC board and the heat can vary as the input voltage changes. For the inductor, depending on the physical size, type of core material and the DC resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board. 9
Package Information SOP8 Package Outline Dimensions 10
Design Notes 11